In one embodiment apparatus is disclosed for taking up and paying out first and second ends of an endless loop of tape (37,39,41) that has an intermediate section. A first reel (57) connected to the first end carries a first coil (64) of the tape. The first coil (64) extends from the first reel (57) and is normally self-expanding and unwinding so as to unwind itself from the first reel (57). A second reel (58) is connected to the second end for carrying a second coil (65) of the tape (37,39,41). The second coil (65) extends from the second reel (58) and is normally self-expanding so as to unwind itself from the second reel (58). A drum (59) supports both of the first and second reels (57,58) for rotation in the same direction. Pulleys (44,45,49,50,47,48) guide the intermediate section of the tape from the first reel (57) to the second reel (58) for moving a sludge collector (33A,33B). When the drum (59) is rotated in a first rotary direction, the first coil (64) tends to self-unwind from the first reel (57) and the second coil (65) is wound up on the second reel (58) to move the intermediate section of the tape and the sludge collector. Upon rotation of the drum (59) in a second rotary direction, the second coil (65) tends to self-unwind from the second reel (58) to apply tension to the tape (37,39,41) and the first coil (64) is wound up on the first reel (57) to move the intermediate section of the tape and the sludge collector (33A,33B).